Apparatus for vaporizing materials by an electron beam



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APPARATUS FOR VAPORIZING MATERIALS BY AN ELECTRON BEAM Filed Aug. 23, 1963 4 3,258,648 Ice Patented August 23, 1966 3,268,648 APPARATUS FOR VAPURIZING MATERIALS BY AN ELECTRQN BEAM Walter Dietrich, Hanau (Main), Germany, assignor to W. C. Heraeus G.m.b.H., Hanan (Main), Germany, a corporation of Germany Filed Aug. 23, 1963, Ser. No. 304,109 Claims priority, appiication Germany, Sept. 25, 1962, H 46,999 2 Claims. (CI. 13-31) The present invention relates to an electron lens arrangement for electron beam melting or vaporizing apparatus.

It is already known to provide electron beam melting or vaporizing apparatus with permanentarnagnetic or electromagnetic lenses for focusing the electron beam which passes thercthrough upon the material to be melted or vaporized. These known lenses are always mounted near the electron source, ie the cathode, for example, in the electron beam gun which produces the electron beam.

Since such an electron beam gun is located at a considerable distance from the material to be melted or vaporized, the electron beam after being focused in and emitted from the electron beam gun must travel freely through a considerable distance before impinging upon the mate rial. Within this distance the electron beam is no longer influenced by any electron-optical means. For attaining a high power concentration in the melting or vaporizer crucible, it is, however, necessary to provide an electron beam of a very high current density since for reasons of insulation and better screening of the radiation, high voltages are avoided as much as possible. Such a beam of a high perveance has, however, the disadvantage that, because of the mutual repulsion of equal electric charge charriers, the beam will expand and therefore the desired high power concentration at the point of impact upon the material cannot be fully attained. This may result in difficulties when melting or vaporizing material which has a high melting point. A further disadvantage of such a lens arrangement is that a part of the electrons of the beam will impinge upon the edge of the melting or vaporizer crucible which will thereby be damaged. This is especially serious in those cases in which this edge is employed for supporting the crucible. There is still another disadvantage which occurs in electron-beam vaporizing apparatus which are used for producing extremely pure deposits by vaporization. If the electrons impinge upon the edge of the vaporizer crucible which often consists of metal, the material of the crucible will also be vaporized with the result that the vaporized material and the deposits produced thereby will be contaminated.

In electron beam melting furnaces it is also known that for focusing the electron beam upon the material in the crucible a magnet coil may be provided around and coaxially to the crucible. The field of application of such an arrangement is very limited since whenever the crucible is exchanged for another of a different size, shape or cross-sectional area, the magnet coil must also. be changed accordingly. This, however, means that practically for any different crucible a separate magnet coil has to be provided. In order to produce a magnetic field of a suificient strength by means of a magnet coil, such a coil has to have a high number of ampere windings which require a relatively large space. At least in a vaporizer it would be very difficult to place such a coil with the required number of ampere windings around the small vaporizer crucible so as to surround and focus the electron beam. These difiiculties and the expenses involved would be so great that they would outweigh the advantages which might be attained. Obviously, the disadvantages mentioned above which occur in melting furnaces when cruci bles of different shapes, sizes and volumes are to be employed occur to a much greater extent in Vaporizers since the small crucibles of the latter are changed much more frequently for others of a different size, shape or volume.

It is an object of the present invention to overcome the above-mentioned disadvantages of the known electron beam melting and vaporizing apparatus and to insure a high concentration of power in a crucible of either of such apparatus.

According to the invention this object has been attained in an extremely simple manner and at a low cost by providing a novel electron lens arrangement for electron beam melting or vaporizing apparatus which consists of a magnetic lens which is adapted to focus an electron beam which is directed upon the material to be melted in the crucible. This novel electron lens arrangement according to the invention consists of a magnetic yoke lens which is mounted in the immediate vicinity of the crucible so that the edge of the crucible will be located closely adjacent to the magnetic poles of the yoke lens, that is, either closely above or below or between these poles. The yoke lens may be a permanently magnetic lens which is preferably adjustable by means of a magnetic shunt, or an electromagnetic lens with one or more field coils. When speaking of an electromagnetic yoke lens, such a lens is meant which consists of a field coil and a magnet yoke with pole pieces, but in which, contrary to a conventional electromagnetic lens, the field coil does not surround the electron beam. The pole pieces may be either rigidly secured to the yoke of the lens or be removable therefrom to permit them to be exchanged. By employing pole pieces which are not axially symmetrical, it is possible thereby to vary the cross-sectional shape of the electron beam in the manner as may be desired. According to a preferred embodiment of the invention, the yoke lens is also used as a means of support for the melting or vaporizer crucible. The yoke lens according to the invention also has the advantage that, if necessary, it may be easily provided with cooling means. Still more important are, however, the advantages of the lens arrangement according to the invention that the pole pieces of the yoke lens may be made very thin and fiat and that the field coil or coils may be mounted far away from the crucible either within or outside of the vacuum vessel which forms the melting or vaporizing chamber. Thus, in the immediate vicinity of the crucible there will only be flat pole pieces of the lens and there are no expensive coils required as in the known arrangements. If the crucible has to be replaced by another of a different shape, size or cross-section, the yoke lens may be very easily adapted to the different conditions by exchanging the pole pieces on the yoke of the lens for a different kind. The more voluminous parts of the yoke lens, however, namely the field coil or coils and their associated yoke-s therefore do not have to be replaced by others. but they remain firmly secured in place within or outside of the vacuum vessel. The use of a yoke lens for refocusing or pointing an electron beam which is directed upon the crucible has still another advantage. By making the pole pieces which are connected to the yoke of the lens of a particular design and shape, for example, by not making them axially symmetrical, the cross-sectional shape of the electron beam may be varied in the particular manner as desired. This is of particular importance in vaporizing apparatus in which the small crucibles are usually of an elongated shape. It is then possible, for example, by providing pole pieces of a suitable design to change an electron beam of a circular cross section which is directed upon the yoke lens to one of an elongated, substantially elliptical cross section. By making the pole pieces of the yoke lens of a flat shape, the further advantage is also attained in vaporizing apparatus that the electron beam may be accurately refocused without danger that the focusing device will cause any undesirable shadow effect.

The various features and advantages of the present invention will become more clearly apparent from the following description thereof which is to be read with reference to the accompanying diagrammatic drawings in which:

FIGURE 1 shows a cross section of an electromagnetic yoke lens and a single field coil;

FIGURE 1a shows a plan view of the electron lens arrangement according to FIGURE 1;

FIGURE 2 shows a cross section of another electromagnetic yoke lens with two field coils; while FIGURE 3 shows a cross section of a permanent-magnetic yoke lens according to the invention.

According to FIGURES l and 2 of the drawings, the electron lens arrangement according to the invention is intended for refocusing or pointing an electron beam 3 upon the material 2 in a vaporizer crucible 1 for heating and vaporizing this material. As conventional in vaporizing apparatus, the crucible 1 which is usually of an elongated shape is enclosed in an evacuated vessel which also contains the body upon which the vaporized material is to be deposited. The details of the vaporizing apparatus are not illustrated in the drawings since their features are well known and are not directly concerned with the invention. According to the invention, the yoke lens is mounted so that its magnetic poles north and south are located closely above the upper edge of the vaporizer crucible 1. The yoke lens according to this embodiment of the invention essentially consists of a field coil 4 which is located at a considerable distance from the vaporizer crucible 1 and is energized by a source of current 5, and further of the yoke 6 which carries the flat pole pieces 7 and 8. The field coil 4 may be mounted either within or outside of the vacuum vessel, not shown. The electron beam 3 which is focused by conventional means at the electron gun, not shown, and is directed upon the crucible 1 is focused once more or pointed by the magnetic field which is formed between the magnet poles north and south, that is, the pole pieces 7 and 8. It is, of course, possible to vary the refocusing of the electron beam 3 by varying the strength of the electric current with which the field coil 4 is energized.

FIGURE 2 illustrates a modification of the electron lens arrangement according to the invention which differs from the arrangement according to FIGURES 1 and 2 by the fact that the' edge of the elongated vaporizer crucible 1 is located between the fiat magnetic poles north and south of the yoke lens, that the pole south is also employed for supporting the crucible 1, and that two field coils 4 and 4' are provided. This yoke lens therefore has two separate yokes 6 and 6 which carry the pole pieces 7, 7' and 8, 8'. The field coils 4 and 4 are connected to two sources of current 5 and 5, although it is also possible to connect both field coils 4- and 4' to only one source of current. The effect of the yoke lens according to FIGURE 2 is the same as that of the yoke lens according to FIGURE 1 insofar as the electron beam 3 is likewise refocused or pointed. It has, however, the additional advantage that, due to the provision of two field coils, there is a greater possibility of vary the influence upon the electron beam.

FIGURE 3 shows an electron lens arrangement according to the invention in which a permanent-magnetic yoke lens is employed. The edge of the vaporizer crusible 1 is located above the two magnetic poles N and S. For producing the magnetic field, there are in this case two permanent magnets 9 and 9 provided which carry the yokes 6 and 6 which, in turn, carry the fiat pole pieces 7, 7' and 8, 8'. The two permanent magnets 9 and 9' are likewise mounted at a considerable distance from the vaporizer crucible 1 and, according to a preferred embodiment of the invention, they may be shifted more closely to or further away from the crucible by suitable means as indicated diagrammatically at 10 and 10'. A further adjustment of this lens arrangement may also be provided by means of a magnetic shunt. Although in FIGURE 3 there are two permanent magnets provided, it is also possible to provide only a single permanent magnet in a manner similar as in the electrode lens arrangement according to FIGURE 1.

Although the embodiments of the invention as illustrated in FIGURES 1 to 3 relate to vaporizing apparatus, the invention may be applied in a similar manner also to an electron beam melting apparatus which then only requires the vaporizer crucible which may, for example, be of an elongated shape to be replaced by a melting crucible.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim 1. In an apparatus for vaporizing material by an electron beam, the combination of a crucible containing said material to be vaporized by said electron beam, said crucible having an upper edge portion, a magnetic yoke lens comprising magnetic poles disposed one above the other closely adjacent to said crucible so that said upper edge portion of said crucible is disposed closely adjacent to said magnetic poles of said yoke lens, and means remotely arranged from said crucible for providing a magnetic field between said magnetic poles, said magnetic field influencing said electron beam only on a small length in the vicinity of said upper portion of said crucible, said crucible including means mounting said crucible in such a position that its upper edge portion is disposed between said magnetic poles of said yoke.

2. In an apparatus for vaporizing material by an electron beam, the combination of a crucible containing said material to be vaporized by said electron beam, said crucible having an upper edge portion, a magnetic yoke lens comprising magnetic poles disposed one above the other closely adjacent to said crucible so that said upper edge portion of said crucible is disposed closely adjacent to said magnetic poles of said yoke lens, and means remotely arranged from said crucible for providing a magnetic field between said magnetic poles, said magnetic field influencing said electron beam only on a small length in the vicinity of said upper portion of said crucible, said pole pieces being secured to said yoke, and said crucible including means mounting said crucible in such a manner that its upper edge portion is disposed closely adjacent to said pole pieces and said crucible is supported by at least one of said pole pieces.

References Cited by the Examiner UNITED STATES PATENTS 2,305,761 12/1942 Borries et al 250-495 X 2,932,588 4/1960 Frank. 3,040,112 6/1962 Smith l33l 3,068,309 12/1962 Hanks 2l912l X 3,170,019 2/1965 Hanks 219-121 X FOREIGN PATENTS 720,927 5/1942 Germany.

RICHARD M. WOOD, Primary Examiner.

JOSEPH V. TRUHE, Examiner. 

1. IN AN APPARATUS FOR VAPORIZING MATERIAL BY AN ELECTRON BEAM, THE COMBINATION OF A CRUCIBLE CONTAINING SAID MATERIAL TO BE VAPORIZED BY SAID ELECTRON BEAM, SAID CRUCIBLE HAVING AN UPPER EDGE PORTION, A MAGNETIC YOKE LENS COMPRISING MAGNETIC POLES DISPOSED ONE ABOVE THE OTHER CLOSELY ADJACENT TO SAID CRUCIBLE SO THAT SAID UPPER EDGE PORTION OF SAID CRUCIBLE IS DISPOSED CLOSELY ADJACENT TO SAID MAGNETIC POLES OF SAID YOKE LENS, AND MEANS REMOTELY ARRANGED FROM SAID CRUCIBLE FOR PROVIDING A MAGNETIC FIELD BETWEEN SAID MAGNETIC POLES, SAID MAGNETIC FIELD INFLUENCING SAID ELECTRON BEAM ONLY ON A SMALL LENGTH IN THE VICINITY OF SAID UPPER PORTION OF SAID CRUCIBLE, SAID CRUCIBLE INCLUDING MEANS MOUNTING SAID CRUCIBLE, IN SUCH A POSITION THAT ITS UPPER EDGE PORTION IS DISPOSED BETWEEN SAID MAGNETIC POLES OF SAID YOKE. 